#!/bin/sh

file=$(readlink -f "$1")
dir=$(dirname "$file")
base="${file##*/}"
ext="${base##*.}"

ffmpeg -i $file  -af "pan=stereo|FL < 1.0*FL + 0.707*FC + 0.707*BL|FR < 1.0*FR + 0.707*FC + 0.707*BR" "$dir/stereo-$base.$ext"